In the case both of conventional telephone networks employing time-division multiplexing and of internet telephony, users are increasingly confronted with undesired telephone advertising—referred to in technical circles also as spam. Said undesired telephone advertising is executed by automatic callers with the aid of which call numbers are dialed randomly or selectively, with its being attempted by means of stored, pre-established voice information to sell the called user goods or services or to induce the user to call back to an expensive premium service having in Germany, for example, the prefix 0190.